This invention generally relates to apparatus and methods for cleaning surfaces and more particularly relates to an apparatus and a method for remotely decontaminating, cleaning, or polishing the surfaces of nuclear reactor cavity walls, wherein the apparatus includes brush means for cleaning the surface of the wall, drive means connected to the brush means for rotating the brush means to clean an area of the surface of the wall, means connected to the brush means for simultaneously orbiting the brush means as the brush means rotates to clean a larger area of the surface of the wall. The apparatus may alternatively include a polisher for polishing the surface of the wall.
A nuclear reactor, which is a device for producing heat by fissioning nuclear fuel, must be periodically refueled during what is commonly referred to as a refueling outage. Not only is the reactor refueled during the refueling outage, but maintenance activities may also be performed at that time. During the refueling outage, workmen come into close proximity to the reactor cavity, in which the reactor resides, for refueling and for maintaining the reactor. However, during operation of the nuclear reactor, the reactor cavity walls, which typically have a stainless steel facing, may have become contaminated with radioactive particulate matter adhering to the walls. Hence, to reduce the amount of radiation exposure to the workmen, the reactor cavity walls are typically cleaned before refueling and maintaining the reactor.
Decontamination of reactor cavity walls has been obtained by lowering a workman into the reactor cavity to clean the cavity walls. In one method of cleaning the cavity walls, the workman uses cloths soaked in a suitable cleaner, such as acetone, to manually wipe the surface of the reactor cavity wall for removing the radioactive contaminants. Another method of cleaning reactor cavity walls includes lowering a workman, equipped with a high pressure water hose, into the reactor cavity. The workman then holds the high pressure water hose and directs high pressure water spray against the surface of the wall to remove the contaminants. However, the high pressure water spray impinging the surface of the wall may direct some of the radioactive contaminants from the wall onto the workman, thereby increasing the risk of radiation exposure to the workman. In any case, both methods recited above for decontaminating the walls of the reactor cavity are necessarily time consuming and may result in increased risk of radiation exposure to the workman because workman must be lowered into the cavity. Moreover, reducing the time the workman remains in the cavity, in order to reduce the amount of radiation exposure to that workman, will necessarily result in less surface area being adequately cleaned. In addition, using several workmen to clean the reactor cavity, in order to reduce the radiation exposure to any one workman, is impractical for reasons including increased labor and material costs to perform the decontamination. Therefore, it would be desirable if the reactor cavity walls were cleaned remotely without the need for a workman in the reactor cavity.
A device for remotely decontaminating a nuclear reactor cavity is disclosed by U.S. Pat. No. 4,436,694 issued Mar. 13, 1984 in the name of Michael Vassalotti et al. entitled "Nuclear Reactor Cavity Decontamination Machine". The Vassalotti et al. patent is directed towards a device for decontaminating the walls of boiling water reactor cavities and storage pits. This patent discloses an apparatus comprising a chassis which has wheels in rolling contact with the floor of the cavity and first and second curb wheels in rolling contact with a raised curb surrounding the periphery of the cavity. The apparatus directs high pressure water spray onto the surface of the wall for cleaning the wall. The apparatus is run along the curb, thereby cleaning a horizontal strip of the wall. This operation is repeated until the entire wall is cleaned. The Vassalotti et al. patent, however, does not appear to disclose brush means for cleaning the surface of the wall. Moreover, the Vassalotti et al. patent does not appear to disclose an apparatus for suitably polishing the surface of the cavity wall.
Another device for remotely cleaning reactor cavity walls is disclosed by U.S. Pat. No. 4,351,132 issued Sept. 28, 1982 in the name of Roland Molin entitled "Machine for Cleaning Vertical or Inclined Surfaces". The Molin device comprises at least one roller brush supported by a frame and further comprises a fluid distribution means arranged on the frame for directing jets toward the cavity wall. Although the Molin patent may disclose at least one roller brush and fluid distribution means, the Molin patent does not appear to disclose brush means which rotates for cleaning an area of the surface and which also simultaneously orbits as it rotates for cleaning a larger area of the surface of the wall. Moreover, the Molin patent does not appear to disclose an apparatus for suitably polishing the surface of the cavity wall.
Therefore, while the prior art discloses various devices for remotely cleaning reactor cavity walls, the prior art does not appear to disclose an apparatus and a method for decontaminating or cleaning the surface of reactor cavity walls, wherein the apparatus includes brush means for cleaning the surface, drive means connected to the brush means for rotating the brush means to clean an area of the surface and means connected to the brush means for simultaneously orbiting the brush means as the brush means rotates to clean a larger area of the surface of the wall. Moreover, the prior art does not appear to disclose a polisher for polishing the surface of the cavity wall.
Consequently, what is needed are an apparatus and a method for decontaminating, cleaning or polishing the surface of reactor cavity walls, wherein the apparatus includes brush means for cleaning the surface of the wall, drive means connected to the brush means for rotating the brush means to clean an area of the surface of the wall, means connected to the brush means for simultaneously orbiting the brush means as the brush means rotates to clean a larger area of the surface of the wall. The apparatus may alternatively include a polisher for polishing the surface of the cavity wall.